In commerce and industry today, the useful life of a variety of items may be extended and/or preserved by providing one or more suitable inhibitors. An inhibitor is a compound or group of compounds which can slow or negate the rate of corrosion, decomposition, degradation and/or spoilage of a given item due to, for example, corrosion or oxidation. For example, certain metals are prone to corrosion and/or tarnishing. A suitable inhibitor, in such a case, would be a compound (or group of compounds) which acts as a corrosion inhibitor thereby protecting a desired item or items from the adverse effects of its ambient environment.
Among the common indications of corrosion manifested in useful metallic articles is oxidation, pitting, tarnishing, mottling or discoloration of the surfaces of these items. These manifestations occur in metallic articles, particularly when exposed to chlorides, SOx, CO2, H2S, oxygen and/or water, in either gaseous or liquid phase. Additionally, sulfides, chlorides (or chlorine), carbon dioxide and/or sulfur dioxide may cause corrosion or tarnishing problems as well. Inasmuch as both oxygen and water, including water vapor, occur normally and are available in nature, it is normally necessary to take precautions against corrosion in metal containing, or metallic, items during normal use. Metals which are frequently found to be susceptible to corrosion under normal atmospheric and ambient conditions include, but are not limited to, iron, aluminum, and alloys of these metals. Additionally, suitable protection may also be needed for hybrid articles (i.e., articles that are partially metal or contain a significant amount of metal therein) such as reinforced concrete.
In view of the widespread need for protecting various articles from corrosion, whether the articles be metallic or otherwise, a variety of short-lived systems have been utilized. For example, the use of VCI capsules permits a producer/manufacturer to place a VCI capsule in an existing packaging system or enclosure (e.g., a storage tank), without having to redesign same, while still making sure that the products contained within the packaging are protected against corrosion, tarnishing or some other form of degradation. However, VCI based systems are generally limited to protecting metallic surfaces, or other corrosion prone surfaces, that are in contact with air, some other gas, or a gaseous atmosphere.
Alternatively, cathodic corrosion management systems permit one to mitigate and/or reduce the rate of corrosion that occurs in hybrid structures such as reinforced concrete and in metallic structures such as storage tanks (both above and below ground varieties). Such cathodic systems have drawbacks including the ability to only protect those metal parts, or surfaces that are in current contact with the cathodic system, or in the case of electrolyte-based cathodic systems only those surfaces that are fully immersed in a suitable electrolyte. Thus, in the case of cathodic systems, various surfaces remain unprotected (e.g., surfaces in contact with vapor spaces, air, or some other gas).
In other instances, soluble corrosion inhibitors have been utilized to protect, for example, a liquid that is being stored within a storage tank. Such systems suffer from various drawbacks including: (1) a situation where the amount of soluble corrosion inhibitor necessary to provide protection to the tank leads to contamination of the liquid stored therein; and/or (2) the situation where the soluble corrosion inhibitor is only effective in protecting against corrosion that occurs in one discrete portion of a liquid in a storage tank (e.g., water or some other aqueous liquid in an oil storage tank).
Such methods, although effective, are not suitable for all tanks, containers, and/or closed systems which may need to be protected. Additionally, such methods have service lives which are not suitable for applications, in which a long service life is necessary, for example, the use of cathodic systems to protect storage tanks which hold petroleum products. Furthermore, the replenishment of certain currently used systems, such as cathodic systems, is both expensive and difficult.
Turning to storage tanks, and specifically above ground storage tanks, multiple environmental factors affect corrosion of such storage tanks, and in particular, if present, the double-bottom internal surfaces of such tanks. Such factors include, but are not limited to, the age of the tank, the surface area exposed or in contact with at least one corrosive environment, the water saturation level of the sand inside the tank bottom, and the occurrence of one or more vapor spaces. Since changes in the relative importance of these factors during the lifetime of a storage tank can not be predicted, current technologies do not provide adequate protection against all existing factors.
Existing methods have the following disadvantages: (1) electrolyte-based cathodic protection alone works only when any internal metallic surfaces of the tank to be protected, (e.g., the double bottoms) are fully immersed in the electrolyte (i.e., no vapor spaces); (2) soluble corrosion inhibitors alone are effective only in relatively high concentrations and only when any internal metallic surfaces of the tank to protected, (e.g., the double bottoms) are fully immersed in the solvent carrying the desired soluble corrosion inhibitor (i.e., no vapor spaces); (3) electrolyte-based cathodic protection in combination with one or more soluble corrosion inhibitors, where the one or more soluble corrosion inhibitors are present in the electrolyte of the cathodic system, are efficient, but again only function efficiently when any internal metallic surfaces of the tank to protected, (e.g., the double bottoms) are fully immersed in the electrolyte (i.e., no vapor spaces); and (4) filling and draining of the tank causes the tank bottom to flex and undulate which causes vapor spaces to be created and leads to one or more of the above drawbacks. Since these vapor spaces may be uniform or in isolated pockets, they can cause the electrolyte of an electrolyte-based cathodic corrosion prevention or mitigation system to lose contact with the upper metallic surface thereby rendering the electrolyte-based cathodic corrosion prevention or mitigation system and soluble corrosion inhibitor system ineffective.
Additionally, once a electrolyte-based cathodic corrosion prevention or mitigation system with a soluble corrosion inhibitor therein has been implemented, the efficiency of the system cannot be modified while the tank is in operation. In such situations, it becomes necessary after a period of time to stop using such a tank in order to replenish and/or service such a system.
Thus, there is a need in the art for a system and method which provides flexible corrosion protection in light of, or in response to, a changing environment and/or application conditions, while at the same time permitting the flexible delivery of differing amounts of one or more volatilizable compounds.